One of the greatest monster movies of all time and the one that brought director Steven Speilberg to prominence. This film is excellent for three reasons. First, The acting was superb, particularly the interplay between Roy Scheider, Richard Dreyfuss and Robert Shaw. It doesn't hurt that they are played by three highly skilled actors and supported by a script that snaps with great dialog and, for about the last forty minutes, non-stop tension. The most notable example is the long (but not drawnout) scene in the Orca when the three discuss their fears and motivations for catching the shark.
Second, the deirection by Spielberg. Spielberg takes a lot of time for character development, but he doesn't lump it all together at the beginning of the filmScenes like Brody's son mocking Brody's expressions at the dinner table, or Quint's speech about why he hunts sharks, are crucial to understanding the motivations of characters, but Spielberg makes sure they come at times where a release of tension is needed.
Finally, the ingenious music that John Williams composed for the film, especially the two note theme that announces the impending arrival shark, which has become part of our pop culture. Other production aspects deserve mentions as well, from Bill Butler's superb cinematography to the mechanical shark itself, which, despite the well-known tales of it not working most of the time, still looks menacing.
Jaws is one of the best monster movies ever made simply because it takes time to explore the human side of its story. It is a penetrating drama, a kind of throwback to 1950's monster films. It influenced films such as Alien and Deep Blue Sea, whether in the general construction of story, the setting, or more literal takes on a monster in a closed environment. Even if this weren't the case, Jaws would still be essential viewing for anyone serious about film.